Electric smelting furnace electrode having a wooden core

ABSTRACT

One or more wooden logs are introduced into the central region of smelting furnace electrodes as they are being formed of paste to produce an electrode that has a non-conductive center and an outer conducting sheath of baked and hardened carbonaceous material.

United States Patent 1 Persson 51 Feb. 6, 1973 [54] ELECTRIC SMELTING FURNACE [56-] References Cited -g 6%% HAVING A WOODEN UNITED STATES PATENTS 1,150,021 8/1915 Favier ..13/18 [75] Inventor John Persson Gibsoma 2,603,669 7/1952 Chappell ..l3/18 [73] Assignee: Pennsylvania Engineering Corpora- Primary Examiner-Roy N. Envall, Jr. 2] Filed: Aug. 27, 1971 Attorney-Wiviott & Hohenfeldt [21] Appl. No.: 175,496 ABSTRACT v One or more wooden logs are introduced into the cen- -[52] US. Cl. ..]3/l8 "a! region of smelting furnace electrodes as they are [5 lllt. Cl: I t r ..H051) formed of paste to reduce an [53] Field of Search 13/1 8, 185 OD p has a non-conductive center and an outer conducting sheath of baked and hardened carbonaceous materiali' 7 Claims, 5 Drawing Figures P/xmmum 61973 3.715.439 1 SHEET 1 0F 2 INVENTOR FIG] JOHN A. PERSSON f ATTORNEYS PATENTEUFEB 6197s saw 2 or 2 INVENTOR JOHN APERSSON ATTORNEYS hereinafter.

7 BACKGROUND OF THE INVENTION which is inherent in alternating current conductors.

The central region or core of an electrode conducts little current, if any. Nevertheless, it had' been the custom to make the central region of both prebaked and selfbaking electrodes of the same quality paste as that used in the outer more conductive peripheral layer. This is an obviously inefficient use of the costly electrode forming paste.

The amount of electrode material consumed in an electric furnace represents a significant portion of the cost of making a ton of steel. A skilled furnace designer will design a furnace system to minimize electrode consumption or, at least, to-minimize the total cost of the electrodes consumed. The least expensive electrode forming paste isfthat which has a high non-graphitic carbon content and, of course, the most expensive is that which has a high content of carbon which is in the more highly conductive and more thermally stable graphltic form. In any event, the least expensive grade of electrode material that will satisfy the operating conditlons in the furnace reasonablywell is usually chosen but in most cases it .would be advantageous to use the material with highgraphite content if it were not so expensive.

Presently, electrode pastes are made by calcining petroleum or asphalt ,cokes in either, a fossil fuel fired kiln or an electric resistive heating furnace at below 1590" where graphitization transformation begins. TIIIS essentially ungraphitized comminuted calcined carbon s mixed with bonding materials such as pitch or tar In a heated state or is fed directly into the electrode columns. The least amount of bonding material is used so that the electrode has the highest carbon content possible consistent with strength.

In order to transform more of the carbon to graphite and thereby secure a higher quality paste, the calcining process must be carried out at temperatures well above l 500 C. for an extended period of time. Generally, h gh grade electrode pastes are made of electrically calclned anthracite which has been calcined in the temperature range where graphitization takes place. The large amount of electric energy used for obtaining graphitlzed carbon results in a costly paste but which has high electric conductivity and mechanical strength.

SUMMARY OF THE INVENTION portions with rigid but non-conductive material such as wood logs.

I 'Another object of this invention is to reduce the weight of electrodes without sacrificing strength or conductivity by substituting wood for higher cost'paste n the center portion of the electrode.

How the foregoing and other more specific objects are achieved will appear from time to time throughout the course of a description of an illustrative embodiment of the invention which will be set forth Briefly stated, the invention is most advantageously used in connection with self-baking electrodes. The electrode paste is fed into a casing which is supported above an electric furnace and is open at its upper end. The paste is usually in the form of solidified blocks which melt and eventually bake and solidify into a cylindrical form as the paste advances toward the hot furnace. In accordance with the invention, one or more cylindrical wooden logs are inserted axially into the open end of the casing so that the paste will fuse around the logs and form an outer conductive sheath. The wood chars as it nears the furnace and reduces the overall weight of the electrode because the density of the wood after it has become charred is less than that of the baked paste. Thermal cracking of the hydrocarbons provides additional carbon in the interstices of the-already baked electrodes resulting in greater electric conductivity and compressive strength.

An embodiment of the invention will now be described in reference to the drawings.

DESCRIPTION OF THE DRAWINGS DESCRIPTION OF PREFERRED EMBODIMENT In FIG. 1 the schematically represented electric furnace is generally designated by the reference numeral 10. The interior furnace bottom 11, the side walls 12 and the top 13 were made out of the customary refrac-. tory materials.

One electrode forming device, generally designated by the numeral 14, is shown associated with the furnace for the sake of illustrating the invention. This electrode forming device has been widely used and is sufficiently well known to obviate describing it in detaiLIIowever, the forming device has several coaxial cylindrical sections l5, l6 and 17 in which the paste that is introduced at the top of the device becomes progressively'hotter as it approaches the furnace and bakes out or solidifies. A solid cylindrical electrode 18 so formed extends into the furnace in a well known manner as shown.

At the top end of electrode forming device 14 are a pair of holding bands 19 and 20 which are coaxially arranged and interconnected with several hydraulic position 20 while the electrode is held by its main clamp 19. When clamp 20 has reached its uppermost position it closes and clamp 19 opens. Then the elec-' trode is lowered by the hydraulic cylinder 21 and the holding clamp -19 closes after the-slipping band has reached its original position. For presentpurposes, it is sufficient to observe that uncured blocks of paste are introduced into the top end of electrode forming device 14 and that a solidified baked electrode 18 emerges from the bottom. The hoist which handles the paste material at the upper end of forming device 14 is not shown because it is conventional. The same hoist may be used to handle and insert the wooden cores into the center of the electrode in accordance with the invention.

FIG. 2 shows a top view of the electrode forming device 14. It comprises a hollowcasing 26 from which a plurality of fins 27 project radially inwardly. By way of example, the radial dimension of these fins may be about inches and their axial length may be about 6% feet in a device that is adapted for forming electrodes having nominal 45 inch outside diameter. There may be 10 such fins equiangularly spaced which means that they would be about 36 apart. The blocks of uncured electrode paste are dropped into casing 26 in the interspaces 28 between, successive fins 27. As the paste material absorbs heat it melts and fills the existing cavities. Of course, as the paste progresses downwardly, it absorbs heat in which case the paste in annular region 29 and the fin interspaces 28 merge into a homogeneous viscous mass. In accordance with one aspect of the invention, a wooden log such as 30 is introduced throughthe top of casing 26 and blocks of paste are deposited around the log. The molten paste in the casing and the melting blocks of paste eventually encase the log. Thus, cylindrical wooden log 30 constitutes a core which fills a space that would normally be occupied by electrode paste. As the paste descends in electrode forming device 14, additional blocks of paste and cylindrical wooden logs 30 are inserted as required to produce an electrode that has a substantially continuous central core surrounded by a sheath of carbonaceous electrode material.

The vertical sectional view of an electrode made in accordance with the new method may be seen in FIG. 3

which illustrates how the central wooden core 30 is surrounded by a homogeneous annular sheath of conductive paste which is marked 31.

For a small size self-baking electrode, such as is shown in FIG. 3, it is feasible to use single cylindrical wooden logs 30 because logs of adequate size are commercially available. For instance, in an electrode hav- For larger self-baking electrodes such as those having outside diameters of up to 75 inches a central wooden core having a diameter of about 40 inches may be used. This leaves a conductive paste annulus of about l7 inches in radial thickness which is adequate to conduct the maximum current in an electrode of this size. However, wooden logs having a diameter of about 40 inches are not readily available and, if they were, would be extremely expensive. Consequently, for large size electrodes, the use of a plurality of smaller diameter wooden logs is recommended. Thus, relatively low cost logs of smaller diameter, such as about 6 inches may be bundled or grouped as in FIG. 5 to produce a composite core which may be easily handled and inserted in the central region of the electrode. Theshort logs may also be introduced individually to form a group at the same level within the electrode forming device. FIG. 5 shows a bundle of logs 33, which may or may not be of equal diameter, bound together with metal straps 34. The lengths of the various logs need not be exactly the same. Bundles such as this are deposited endwise into the upper open end of electrode forming device 14 and consecutively to form a wooden core that is continuous over the length of the electrode. A fragmentary section of an electrode core formed with bundles of logs 33 is shown in FIG. 4 where one may also see that the logs are surrounded by a conductive sheath of electrode material 35.

For the small size self-baking electrodes which are commonly used, that is, for electrodes which have an outside diameter of about four feet, the use of central wooden cores permits a saving of 15 percent or more of electrode forming paste. in large size electrodes, such as those having outside diameters of about inches, a saving of electrode paste on the order of 30 percent can be obtained. The cost of the logs is very small compared with the cost of the electrode forming paste even if the largest size logs are used. However, considerable economy can be effected by using bundles of smaller logs or bundles of rectangular or square or otherwise cross sectionally shaped long wooden pieces in place of logs. The basic concept of the invention is fulfilled by using elongated wooden pieces singly or in bundles or groups as a core for an electrode made of carbonaceous paste which cases the core and bonds with it.

Those skilled in the art will appreciate that the principles of the invention may be applied to making prebaked electrodes as well as to self-baking electrodes and that in connection with making prebaked electrodes the wooden members may be inserted in the mole form concurrently with the introduction of melted electrode paste after which the pliable paste cylinder may be removed from the mold in the customary fashion and baked.

Although embodiments of the invention have been described in considerable detail, such description is to be considered illustrative rather than limiting, forthe invention may be variously embodied and is to be limited only by interpretation of the claims which follow.

lclaim:

l. in apparatus of the class wherein an electrode is formed in a casing having upper and lower end openings and which extends toward an electric arc furnace so that electrode paste introduced into the upper opening melts in a region intermediate the openings and bakes and cures to form hardened electrode material near the lower opening due to heat conducted from that portion of the electrode which emerges from said casing into said furnace, the combination with said electrode of a wooden core extending substantially centrally of said casing through said paste in the regions where said paste is introduced and where it is molten and where it emerges from said casing and enters said furnace.

2. The invention set forth in claim 1- wherein:

a. said wooden core is comprised of a series of single elongated wooden elements disposed axially of each other. r H

3. The invention set forth in claim 1 wherein:

a. said wooden core is comprised of groups of when the paste melts due to heat derived from the furnace said paste flows around each wooden element and encases it.

5. The method set forth in claim 4 wherein:

a. said electrode is continuously advanced toward said furnace to absorb sufficient heat for charring said wooden elements consecutively before they enter the furnace.

6. The method set forth in claim 4 wherein:

a. the wooden elements are substantially the same length and are inserted to form groups which are disposed in end-to-end fashion in the central region of the electrode.

' 7. The invention set forth in claim 4 wherein:

a. the electrode forming paste is in the form of solid blockswhen being introduced into the upper end of the electrode forming device. 

1. In apparatus of the class wherein an electrode is formed in a casing having upper and lower end openings and which extends toward an electric arc furnace so that electrode paste introduced into the upper opening melts in a region intermediate the openings and bakes and cures to form hardened electrode material near the lower opening due to heat conducted from that portion of the electrode which emerges from said casing into said furnace, the combination with said electrode of a wooden core extending substantially centrally of said casing through said paste in the regions where said paste is introduced and where it is molten and where it emerges from said casing and enters said furnace.
 1. In apparatus of the class wherein an electrode is formed in a casing having upper and lower end openings and which extends toward an electric arc furnace so that electrode paste introduced into the upper opening melts in a region intermediate the openings and bakes and cures to form hardened electrode material near the lower opening due to heat conducted from that portion of the electrode which emerges from said casing into said furnace, the combination with said electrode of a wooden core extending substantially centrally of said casing through said paste in the regions where said paste is introduced and where it is molten and where it emerges from said casing and enters said furnace.
 2. The invention set forth in claim 1 wherein: a. said wooden core is comprised of a series of single elongated wooden elements disposed axially of each other.
 3. The invention set forth in claim 1 wherein: a. said wooden core is comprised of groups of wooden elements which groups are disposed axially of each other.
 4. A method of forming a self-baking arc furnace electrode comprising: a. introducing unbaked electrode forming paste into the interior peripheral region of the upper end of an electrode forming device from whose lower end an electrode extends into a furnace, and b. inserting wooden elements axially of each other into the central region of the said upper end so that when the paste melts due to heat derived from the furnace said paste flows around each wooden element and encases it.
 5. The method set forth in claim 4 wherein: a. said electrode is continuously advanced toward said furnace to absorb sufficient heat for charring said wooden elements consecutively before they enter the furnace.
 6. The method set forth in claim 4 wherein: a. the wooden elements are substantially the same length and are inserted to form groups which are disposed in end-to-end fashion in the central region of the electrode. 